The present invention relates to cooling for lighting fixtures, and particularly, to cooling features to minimize thermal conduction between the light emitter and light driver and maximize thermal convection cooling of the driver.
Managing the temperature of light sources is often important to performance and longevity. This is particularly true with newer highly efficient lighting technology, for example, light sources such as LEDs or laser diodes. LEDs are generally selected to maximize the light output for a given power consumption at a reasonable cost. Because LED light sources operate at a much lower temperature than typical incandescent light sources, less energy is wasted in the form of heat production. However, LEDs tend to be more sensitive to operating temperature and the lower operating temperatures also provide a much smaller temperature difference between the LED and the ambient environment, thus requiring greater attention to thermal management to transfer and dissipate any excess heat generated by the LED driver and emitter so that the design operating temperature for the components are not exceeded.
As temperatures rise, the efficacy of the LED is reduced, reducing the light output. Also, increased operating temperature of the emitter reduces the lifespan of the LED. While the operating temperature is most critical for the LED emitter, the LED driver also generates and is affected by heat. As the temperature rises within a light fixture housing, raising the driver temperature, the lifespan of the driver is adversely affected causing premature failure. Operating at temperatures above the design limits can also cause LEDs to shift in wavelength providing undesirable shifts to the color of the light generated, can damage the LED junction greatly reduce the longevity and performance, and can potentially cause early complete failure of the LED.
To facilitate dissipation of heat, convection, conduction, and radiation are available modes of heat transfer. Thus, it is helpful to provide a light fixture with features that increase the surface area available for convective heat transfer of the heat generated by the LED to the environment around the light housing, for example, features may include cooling fins. Additionally, because more heat is generally generated by the LED emitter than the driver, it is helpful to ensure the heat transferred from the LED emitter is not transferred to the LED driver by conductive heat transfer. However, in most lighting applications, it is also important to maintain a desirable aesthetic appearance to the lighting fixture, and exposure of fins or other such cooling features and separating the emitter and driver into distinct housings tend to provide the light fixture with an undesirable ‘alien’ appearance and, in outdoor applications, promote trapping of debris on or around the cooling fins.
One design seeking to address these concerns provides a set of fins forming vertical airflow channels between a front emitter section and a rear driver section of the light fixture; however, the fins forming the airflow channels vary in length across the light fixture, are in clear view from the sides of the light fixture, and are recessed from the surface of the light fixture, therefore risking the collection of debris in outdoor applications. Thus, in the case of a linear array of emitters, thermal dissipation away from the emitters will vary depending on location relative to the varying sizes of fins. Additionally, the recess formed by the fins may tend to capture debris in outdoor applications. Furthermore, the visibility of the fins from the sides of the light fixture is undesirable.
Therefore, it is desirable to provide a unitary lighting fixture design that minimizes the thermal conduction between the emitter and driver housings, maximizes cooling by thermal convection for the light emitter, shields the cooling features from as many viewing angles as practical, and minimizes the opportunity for debris to be caught in or around the cooling features.